The invention relates to a method of producing mirrors, and to coated glass substrates incorporating coatings exhibiting a bright silver or chrome appearance.
The light reflecting properties of mirrors are generally provided by a layer of highly reflecting metal, especially silver, aluminum or chromium, applied to a glass or plastics substrate; copper layers are sometimes used as an alternative, but are generally less acceptable because of the strong red tint of the reflected light.
Silver coatings are generally applied to preformed glass plates, in the cold, by wet chemical methods in which a solution of silver salt is applied to the glass surface and reacted with a reducing agent which reduces silver ions present to silver metal which deposits on the glass surface. The silver used is not very durable in use and in practice requires protection by other layers, and these methods are generally unsuitable for application to glass on the production line on which it is formed so that a separate "silvering" line is required to produce the silvered glass.
Aluminum coatings are difficult to apply by chemical methods because of the strongly reducing nature of aluminum metal, and aluminum mirrors are generally produced by deposition methods carried out at low pressure, e.g., by sputtering. Such low pressure methods are essentially batch processes and, like the wet chemical methods used for deposition of silver mirrors, are generally unsuitable for on-line application on the production line on which the glass is made.
Silicon layers have also been used to produce reflecting layers (which, like silver and aluminum layers, are substantially neutral in reflection color) on architectural glazing for aesthetic and solar control purposes. U.S. Pat. Nos. 4,088,471, 4,188,444 and 4,469,045 relate to a continuous chemical vapor deposition method for producing float glass having such a silicon layer, and U.S. Pat. No. 4,661,381 describes a development of that method.